1. Field of the Invention
The present invention is directed to a radio station for mobile radio telephone systems and to a method for the selection of a transmission means in a radio station for mobile communication systems.
2. Description of the Prior Art
Mobile communication systems enable the setup of communication connections to and from mobile subscribers wherein information is transmitted via a radio interface. Various methods for separating the subscribers can be utilized at the radio interface. Such methods include, for example, time-division multiplex, frequency-division multiplex or code-division multiplex methods. A known mobile communication system, for example, is the GSM (Global System for Mobile Communication) mobile radio telephone system.
In mobile radio telephony, the information on the radio interface is transmitted with electromagnetic waves. The waves then become polarized as a result of the geometry and the arrangement of the transmission antenna used to emit the waves. After the transmission of the mobile radio telephone channel which characterizes the radio interface, only a part of the energy of the polarized wave is absorbed by the reception antenna. The received energy is maximized when the polarization of the received wave coincides with the polarization of the reception antenna.
The polarization of the emitted wave is modified due to defractions and reflections in the mobile radio telephone channel. In addition, the angle of inclination of the reception antenna has a critical influence on its polarization. In the case of a mobile subscriber using a hand-held unit, this angle is not predictable and is thus purely random. As a result of these factors, the polarization of the wave and the polarization of the reception antenna generally will not coincide and the mobile receiver usually will be able to absorb only a part of the maximally available energy of the electromagnetic wave.
German Patent Application 196 17 140 7 discloses a polarization diversity that may be utilized for improving the reception in a reception station wherein two or more antennas with different polarization supply a reception station with signals that are at least partially decorrelated. Thereafter, the reception station can make a selection from the reception signals. What is not considered in this reception station scenario, however, is that comparable problems also occur for the communication connection from a base station to a mobile station. Indeed, a polarization diversity is difficult to implement in the mobile station due to the constricted construction possibilities.